The present invention relates to rotary mills. More particularly, the invention relates to an automated system for reliably discharging rotary mills that include liquid in the milling cylinder.
Rotary mills, also known as ball mills, pebble mills, rod mills, or tumble mills, are well known in the art. A traditional rotary mill includes a horizontal rotating cylinder that rotates about a central axis. The cylinder includes grinding media that is generally spherical, cylindrical, or another uniform shape. In the case of milling with a liquid medium, solid target materials are placed along with a liquid medium into the cylinder for milling. The cylinder is rotated, causing the grinding media to tumble along with the target material, with the grinding media abrading and impacting the solid target materials. Continued rotation of the cylinder produces a milled product in the form of particles suspended in liquid media.
Upon completion of the milling process, the milled product is discharged from the cylinder. The cylinder includes an opening with a solid cover that can be manually removed and replaced with a discharge grate, which will retain the grinding media but allow the milled product to pass through.
In the case of a wet milled product, the cylinder can remain stationary if the liquid suspending the product is a low-viscosity fluid, the liquid can flow past the media due to gravity. If, however, the liquid is a non-Newtonian or a high-viscosity liquid, the cylinder can be rotated to discharge the milled product.
Alternatively, the grinding media and milled product can be dumped from the cylinder without the use of a grate, and subsequently separated by a grate, filter, or vibrating sifter.
The rotary mill also includes a discharge housing that surrounds the rotating cylinder to define an annular space between the cylinder and the housing. The housing also includes a collection hopper at its bottom. When the milled product is discharged, as described above, the milled product will enter the annular space and fall into the hopper.
However, the above discharge process can result in dirty conditions, with milled product adhering to the inner surface of the housing as well as the outside of the cylinder. Retrieval of the milled product from the discharge housing can also result in milled product entering the surrounding area. These conditions can reduce the amount of milled product recovered, as well as lead to cross-contamination issues and cleaning problems. In the case of liquid milling, the operator must make and break a liquid piped connection to the discharge housing, exposing the milled product and potential solvent vapors to the surrounding area during this break in the connection.
Accordingly, there is a need for a discharge system that can reliably deliver the milled product from the cylinder while limiting loss of milled product and exposure of the milled product to adjacent areas and operators.